War Plan Red, also known as the Atlantic Strategic War Plan, was one of the color-coded war plans created by the United States Department of War during the interwar period of 1919–1939, covering scenarios related to a hypothetical war with the British Empire
(the "Red" forces). Many different war plans were prepared by mid-level
officers primarily as training exercises in how to calculate the
logistical and manpower requirements of fighting a war, and War Plan Red outlined those steps necessary to defend against any attempted invasion of the United States from British forces. It further discussed fighting a two-front war with both Japan and Great Britain simultaneously (as envisioned in War Plan Red-Orange).https://en.wikipedia.org/wiki/War_Plan_Red